“Early to bed, early to rise（起身）makes people healthy, wealthy and wise（健康，富有，聪明）.” This is an old English saying. Children should have ten hours' sleep every night, or （不然，否则）they can't do their work very well. They will not be wise. The body needs exercise. Walking, running, swimming and playing ball games are all exercise. Exercise keeps the body strong.

在细胞正常分裂的情况下，雄性果蝇精巢中一定含有两个Y染色体的细胞是（ ）

中华民族崇尚“士可杀不可辱”，表明中华民族（    ）

如图所示，用内壁光滑的薄壁细圆管弯的由半圆形APB（圆半径比细管的内径大得多）和直线BC组成的轨道固定在水平桌面上，已知半圆形APB的半径R=1.0m，BC 段L=1.5m．弹射装置将一个质量为1kg的小球（可视为质点）以v₀=5m/s的水平初速度从A点弹入轨道，小球从C点离开轨道随即水平抛出，桌子的高度h=1.25m，不计空气阻力，g取10m/s²，π取3.14，求：